A position sensor is a device that can detect the presence and location of a touch, by a finger or by an object, such as a stylus within an area of an external interface of the position sensor. In a touch sensitive display application, the position sensor enables direct interaction with what is displayed on the screen, rather than indirectly with a mouse or touchpad. Position sensors can be attached to or provided as part of devices with a display, including but not limited to computers, personal digital assistants, satellite navigation devices, mobile telephones, portable media players, portable game consoles, public information kiosks, and point of sale systems. Position sensors have also been used as control panels on various appliances.
There are a number of different types of position sensors/touch screens, such as resistive touch screens, surface acoustic wave touch screens, capacitive touch screens, etc. A capacitive touch screen, for example, may include an insulator, coated with a transparent conductor in a particular pattern. When an object, such as a finger or a stylus, touches or is provided in close proximity to the surface of the screen there is a change in capacitance. This change in capacitance is sent to a controller for processing to determine the position of the touch.
In a mutual capacitance configuration, for example, an array of conductive drive electrodes or lines and conductive sense electrodes or lines can be used to form a touch screen having a plurality of capacitive nodes. A node is formed where each drive and sense electrode overlaps. The sense electrodes are capacitively coupled with the drive electrodes at the nodes. A pulsed or alternating voltage applied on the drive electrode may therefore induce a charge on the sense electrode and the amount of induced charge is susceptible to external influence, such as from the proximity of a nearby finger. When an object touches the surface of the screen, the capacitance change at each individual node on the grid can be measured to determine the location or position of the touch. Interpolation processing of signals from the sense electrode can be used to determine the location of the touch that is in between electrodes or nodes, but it may not be possible to determine the location of such a touch with sufficient accuracy in some situations, particularly if the object making the touch is relatively small, such as a stylus.